Ferromagnetic material and process



United States Patent C) FERROMAGNETIC MATERIAL AND PROCESS LotharHeinrich Brixner, Wilmington, Del., assign'or to E. I. du Pont deNemours and Company, Wilmington, -Del., a corporation of Delaware NoDrawing. Filed Sept. 17, 1957, Ser. No. 684,423

4 Claims. (CI. 2358) This invention relates to a new ferromagneticmaterial.

Ferromagnetic materials might broadly be classified into two groups:those with low coercivities, and those with high coercivities. Materialsof the former type are useful in transformers, magnetic amplifiers,memory cores, and microwave devices. The ferromagnetic materials withhigh coercivities are useful in permanent magnets.

The ferromagnetic material of this invention possesses an exceptionallyhigh intrinsic coercive force, and it is represented by the empiricalformula BaMnFe O This material is prepared by heating for from aboutonehalf hour to two hours at temperatures between 600 C. and 1000 C. FeO and BaMnO, in a mol ratio of 6:1, thus simultaneously forming a newcombination of barium manganese, iron and oxygen with the evolution of/2 mol of oxygen. The product obtained from the heating is then cooled,pulverized and compacted under pressure into a unitary mass of desiredshape by pressing or extruding. This mass is subjected to firing forfrom 2 to hours, at temperatures between 1000 C. and 1300 C. In thepractice of this invention, it is convenient and preferred to usecommercially available reactants of the highest purity. X-ray analysisof the final product fails to indicate the presence of barium oxide, orany known manganese oxide, or other known manganese compounds. Thematerial is crystalline and hexagonal in structure, and it showspronounced magnetic anisotropy. The crystals are characterized by thefollowing cell constants: a=5.88 A., c=23.02 A.

For a clearer understanding of the invention, the following specificexample is given. This example is intended to be merely illustrative ofthe invention and not in limitation thereof. Unless otherwise specified,all parts are by weight.

Example 15.766 g. of BaMnO, and 58.94 g. of Fe O were thoroughly mixedand then passed through a 60-mesh screen. The mixture was fired at 1000C. in air for /1 of an hour in a platinum crucible. After cooling toroom temperature in air, the mixture Was ball milled with ethyl alcohol,dried, and passed through a ZOO-mesh screen. The powder was thenhydrostatically pressed at 190,000 p.s.i. into a rod /2" in diameter by1" in length. This rod was fired at 1150 C. for 4 hours in air, and thenit was air quenched. The material thus produced was a compact rod whichwas useful as a magnet. The product thus prepared had a density of 5.11g./cm. This figure was close to the theoretical value for the material.The rod was then tested for magnetic properties, using a Sanford-Bennetthigh field permeammeter from the Rubicon Company. The cylindrical rodwas butted between the pole pieces of the permeammeter and subjected tothe standard operation for obtaining the demagnetizing curve. Themagnetic properties and resistivity were found to be as follows:

The high resistivity and high coercive force combined with high remanentmagnetization make this new compound very valuable as a permanentmagnetic material for use in such application as television yokes,refrigerator door latches, mechanical couplings, and electrical motorsand generators.

Since it is obvious that many changes and modifications can be made inthe above-described details without departing from the spirit and scopeof the invention, it is to be understood that the invention is not to belimited to said details except as set forth in the appended claims.

I claim:

1. As a composition of matter, the ferromagnetic ma- 11815131 BaMnFe O2. As a composition of matter, the ferromagnetic material BaMnFe O withan intrinsic coercive force of about 3350 oersteds, remanence of 1425gauss, a saturation magnetization of about 1580 gauss, and a resistivityof greater than 10 ohm-cm.

3. A process for producing a ferromagnetic material which comprisesheating at a temperature of about 600 C. to 1000 F. for about /2 hour to2 hours a powdered mixture of Fe O and BaMnO, in a mol ratio of 6:1,cooling the product thus obtained, grinding the product to a powder,compacting the powder into a unitary mass, and heating said mass at atemperature ranging between 1000 C. and 1300 C. for from 2-5 hours, andrecovering a ferromagnetic material.

4. A process for producing a ferromagnetic material which comprisesheating at a temperature of C. for /4 of an hour a powdered mixture ofFe O and BaMnO in a mol ratio of 6:1, cooling the product thus obtained,grinding the product to a powder, compacting the powder into a unitarymass, and heating said mass at a temperature of 1150 C. for 4 hours, andrecovering a ferromagnetic material.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Erchak et al.: American Chemical Society Journal, vol. 68(1945), pp. 2082-2093.

Ionker et al.: Physica XIX (1953), pp. -130.

Gorter: Proceedings of the I.R.E., vol. 43, No. 12 (1955), pp. 1945-73.

1. AS A COMPOSITION OF MATTER, THE FERROMAGNETIC MATERIAL BAMNFE12O21. 